1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly, to a liquid crystal display device to which a MUX circuit is applied to reduce the number of gate driving channels.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device is a display device for displaying a desired image by individually providing data signals in accordance with image information to liquid crystal cells arranged in a matrix format and controlling light transmittance of the liquid crystal cells.
The liquid crystal display device includes a liquid crystal display panel in which liquid crystal cells comprising pixel units are arranged in an active matrix format, and a driver integrated circuit (IC) for driving the liquid crystal cells.
The LCD panel includes a color filter substrate and a thin film transistor array substrate facing each other and a liquid crystal layer formed therebetween.
A signal voltage flowing through a data line is transmitted to liquid crystals by a scanning signal being supplied to a gate electrode in the LCD panel. Because such a signal voltage changes the polarization state of the liquid crystals by stages, varying grey levels may be expressed in the liquid crystal display device.
In addition, the liquid crystal display device is mounted with a driving IC in various ways which is a means for supplying a signal to each line formed at a lower substrate of the LCD panel.
Such a technique can be variously implemented, and, for example, there are COB (chip on board), COG (chip on class), TAB (tape automatic bonding) methods, etc.
Of the methods, the COB (chip on board) method corresponds to a liquid crystal display device according to a segment method or to a low resolution panel. In addition, since the number of leads is small, a driving IC is on a PCB (printed circuit board) and the leads of the PCB are connected to the LCD panel by a predetermined method.
However, as the liquid crystal display device turns into a high resolution liquid crystal display device, it becomes hard to mount a driving IC having a very large number of leads onto the PCB.
On the other hand, by the TAB (tape automated bonding) method, such a problem can be solved by mounting the driving IC on a tape carrier.
Meanwhile, the COG (chip on glass) method has excellent connection stability because a chip is directly mounted on a channel, and enables the fine-pitch mounting of the chip on the channel because no additional connection terminal is required.
In the COG method, a multilayer flexible printed circuit board instead of a printed circuit board comes in contact with the panel by an ACF, thereby supplying an input signal to an IC.
Accordingly, the COG method has an advantage that the costs are reduced and reliability is improved, but it is hard to repair a defect and the size of the panel increases because of a pad region for mounting an IC by the COG method.
The TCP (tape carrier package) method is a package for mounting a driving IC chip on a polymer film.
Such a technique is widely used in a product requiring a light, thin, small package such as a portable telephone as well as an LCD.
In this aspect, a driving circuit of a liquid crystal display device in accordance with embodiments of a related art will be described with reference to FIGS. 1 to 3.
FIG. 1 is a plane view schematically illustrating a small panel according to a chip on glass method in accordance with one embodiment of a related art.
FIG. 2 is a plane view schematically illustrating a large-medium sized panel in accordance with another embodiment of the related art.
FIG. 3 is a module schematic view of a LOG B type in accordance with still another embodiment of the related art.
With reference to FIG. 1, a small LCD in accordance with one embodiment of the related art includes an LCD panel 20 obtained by attaching a lower substrate 10 and an upper substrate 15 to each other, the lower substrate 10 having thereon data lines (not illustrated) formed in a vertical direction and gate lines 30a and 30b formed in a horizontal direction.
In addition, some 30a of a plurality of gate lines 30a and 30b are disposed on part of the lower substrate 10, that is, on a surplus space portion not overlapping the upper substrate 15 which is one side of the LCD panel 20. The other gate lines 30b are disposed on part of the lower substrate 10, that is, on a surplus space portion not overlapping the upper substrate 15 which is the other side of the LCD panel 20. The gate lines 30a and 30b are connected to a gate driving circuit 40 on the lower substrate 15 not overlapping the upper substrate 15. Here, descriptions for the data lines (not illustrated) and a data driving IC to which the data lines are connected are omitted.
Thus, according to the small panel in accordance with one embodiment of the related art, a small QVGA (240*320) panel made with a chip on glass (COG) method requires one hundred and sixty connection lines on the left and right, respectively, of an array outer edge portion.
Accordingly, minimization of the width is required in a small LCD panel. It is difficult to fabricate a compact module because the outer edge portion widen significantly because of a process margin width required for a static electricity preventing circuit (not illustrated), a seal line (not illustrated), an alignment film printing margin or the like in addition to the connection lines.
As illustrated in FIG. 2, a medium-sized LCD in accordance with another embodiment of the related art includes: an LCD panel 60 obtained by attaching a lower substrate 50 and an upper substrate 55 to each other, the lower substrate 50 having thereon data lines 83 formed in a horizontal direction and gate lines 73 formed in a vertical line; a data TCP 85 mounted with a date driving IC (not illustrated) located at one side of the gate lines 73, connected to the data lines 83, and transmitting scanning signals to the data lines 83; and a gate TCP 75 mounted with a gate driving IC (not illustrated) located at one side of the gate lines 73, connected to the gate lines 73, and transmitting scanning signals to the gate lines 73.
In addition, a data PCB 80, a medium connected to the data TCP 85 and transmitting external control signals and data signals, and a gate PCB 70 connected to the gate TCP 75 are included. At this time, an external circuit for controlling the gate driving IC flows to the gate PCB 70 through the data PCB. Here, a gate driving signal flowing through the data PCB 80 using a flexible circuit board (hereinafter, referred to as “FPC”) 90 is transmitted to the gate PCB 70.
Accordingly, in the large-medium sized panel according to another embodiment of the related art, because as channels should be driven as there are gate lines, many gate driving ICs are required.
In addition, because the number of module processes for attaching respective gate driving ICs increases and a gate driving PCB is required, costs for the module processes and the unit cost for the module are increased as the number of driving ICs increases.
Meanwhile, with reference to FIG. 3, there is an existing method such as simplifying module processes using a LOG B type module according to still another embodiment of the convention art. However, even in this case, the number of driving ICs and costs for attachment processes are still increased.
As described, according to a driving circuit of an LCD in accordance with the convention art, the demand arises for development of a new IC chip in which only a shift resister is mounted in the panel because of low reliability of a TFT and limitation of an occupiable area which is caused using a TFT having an enormous channel width, and the remaining function is mounted inside a source driving IC in an existing method of a panel having a gate driving IC therein using an a-Si TFT. Thus, problems occur such as a burden of the chip development and increase in the unit cost.
In addition, when a small panel is fabricated by a method such as a COG (chip on glass), etc not being mounted with a circuit, since lines required for a connection unit between a gate driving IC and a pixel array are required as many as gate lines, an outer edge portion of a module increases in width.